ORBi Collection: Electrical & electronics engineeringhttp://hdl.handle.net/2268/86
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Improving pedestrian detection using motion-guided filteringhttp://hdl.handle.net/2268/203861
Title: Improving pedestrian detection using motion-guided filtering
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<br/>Author, co-author: Wang, Yi; Pierard, Sébastien; Su, Song-Zhi; Jodoin, Pierre-Marc
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<br/>Abstract: In this letter, we show how a simple motion-guided nonlinear filter can drastically improve the accuracy of several pedestrian detectors. More specifically, we address the problem of how to pre-filter an image so almost any pedestrian detector will see its false detection rate decrease. First, we roughly identify moving pixels by cumulating their temporal gradient into a motion history image (MHI). The MHI is then used in conjunction with a nonlinear filter to filter out background details while leaving untouched foreground moving objects. We also show how a feedback loop as well as a merging procedure between the filtered and the unfiltered frames can further improve results. We tested our method on 26 videos from 6 categories. The results show that for a given miss rate, filtering out background details reduces the false detection rate by a factor of up to 69.6 times. Our method is simple, computationally light, and can be implemented with any pedestrian detector. Code is made publicly available at: https://bitbucket.org/wany1601/pedestriandetection.Tue, 29 Nov 2016 09:11:51 GMT3D and stereoscopyhttp://hdl.handle.net/2268/203732
Title: 3D and stereoscopy
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<br/>Author, co-author: Verly, Jacques; Grogna, David; Lejeune, AntoineSat, 26 Nov 2016 08:33:03 GMT3D: a fascinating and powerful technology that has changed the political history of the world and has not finished to surprise ushttp://hdl.handle.net/2268/203647
Title: 3D: a fascinating and powerful technology that has changed the political history of the world and has not finished to surprise us
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<br/>Author, co-author: Verly, JacquesWed, 23 Nov 2016 06:25:35 GMTLaBGen: A method based on motion detection for generating the background of a scenehttp://hdl.handle.net/2268/203572
Title: LaBGen: A method based on motion detection for generating the background of a scene
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<br/>Author, co-author: Laugraud, Benjamin; Pierard, Sébastien; Van Droogenbroeck, Marc
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<br/>Abstract: Given a video sequence acquired with a fixed camera, the generation of the stationary background of the scene is a challenging problem which aims at computing a reference image for a motionless background. For that purpose, we developed our method named LaBGen, which emerged as the best one during the Scene Background Modeling and Initialization (SBMI) workshop organized in 2015, and the IEEE Scene Background Modeling Contest (SBMC) organized in 2016. LaBGen combines a pixel-wise temporal median filter and a patch selection mechanism based on motion detection. To detect motion, a background subtraction algorithm decides, for each frame, which pixels belong to the background. In this paper, we describe the LaBGen method extensively, evaluate it on the SBI 2016 dataset and compare its performance with other background generation methods. We also study its computational complexity, the performance sensitivity with respect to its parameters, and the stability of the predicted background image over time with respect to the chosen background subtraction algorithm. We provide an open source C++ implementation at http://www.telecom.ulg.ac.be/labgen.Tue, 22 Nov 2016 08:44:54 GMTActive Network Management for Electrical Distribution Systemshttp://hdl.handle.net/2268/203499
Title: Active Network Management for Electrical Distribution Systems
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<br/>Author, co-author: Gemine, Quentin
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<br/>Abstract: With the increasing share of renewable and distributed generation in electrical distribution systems, Active Network Management (ANM) has become a valuable option for a distribution system operator to operate his system in a secure and cost-effective way without relying solely on network reinforcement. ANM strategies are short-term policies that control the power injected by generators and/or taken off by loads in order to avoid congestion or voltage issues. While simple ANM strategies consist of curtailing temporary excess generation, more advanced strategies instead attempt to move the consumption of loads to anticipated periods of high renewable generation.
Such advanced strategies mean that the system operator has to solve large-scale optimal sequential decision-making problems under uncertainty. The problems are sequential for several reasons. For example, decisions taken at a given moment constrain the future decisions that can be taken, and decisions should be communicated to the system’s actors sufficiently in advance to give them enough time for implementation. Uncertainty must be explicitly accounted for because neither demand nor generation can be accurately forecasted.
This dissertation presents various research contributions about ANM for distribution systems. These contributions range from the motivation of using a framework of sequential decision-making under uncertainty to the study of computational methods that implement ANM strategies. A particular emphasis is placed on the formulation of the problem, which ultimately falls within the class of Markov decision processes. The modeling of stochasticity is explored and a novel approach that relies on a Gaussian Mixture Model is presented. Computational methods including several relaxations and approximations of multi-period and multi-scenario extensions of the optimal power flow problem with discrete decision variables were considered.; Avec la part croissante de production renouvelable et distribuée dans les réseaux électriques de distribution, la gestion active des réseaux de distribution devient une option crédible pour permettre aux gestionnaires de réseaux de distribution d’opérer leurs systèmes électriques. Les stratégies de gestion active sont des politiques de contrôle à court terme qui modulent la puissance injectée par les générateurs et/ou consommée par les charges afin d’éviter des problèmes de congestion ou de tension. Si les stratégies les plus simples se contentent de réduire les excès temporaires de production, d’autres plus complexes visent plutôt à anticiper les périodes de forte production renouvelable pour y déplacer la consommation des charges.
De telles stratégies signifient que le gestionnaire de réseau doit résoudre des problèmes de prise de décisions séquentielles sous incertitude et de grande taille. Ces problèmes sont séquentiels pour plusieurs raisons. Par exemple, certaines décisions prises à un instant donné contraignent les décisions qui peuvent être prises dans le futur. Les décisions doivent également être communiquées suffisamment à l’avance aux acteurs du système pour leur laisser le temps de les implémenter. L’incertitude doit être explicitement prise en compte à cause de l’imprécision des prévisions de consommation et de production.
Cette dissertation présente des contributions de recherche en gestion active des réseaux électriques de distribution. Ces contributions abordent notamment la motivation du cadre de décisions séquentielles sous incertitude et l’étude des méthodes de calcul qui implémentent les stratégies de gestion active. Une attention particulière est portée sur la formulation du problème, qui est finalement présenté comme un processus de décision markovien. Une approche originale reposant sur un modèle de mélange gaussien est décrite pour représenter l’incertitude. Des méthodes de calcul sont également considérées, en particuliers différentes relaxations et approximations d’extensions multi-périodes et multi-scénarios du problème d’écoulement de puissance optimal avec des variables entières.Fri, 18 Nov 2016 13:05:28 GMTNonlinear Reduced Order Model of a 3-Phase Transformer for Electric Network Simulator Couplinghttp://hdl.handle.net/2268/203473
Title: Nonlinear Reduced Order Model of a 3-Phase Transformer for Electric Network Simulator Coupling
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<br/>Author, co-author: Paquay, Yannick; Bruls, Olivier; Geuzaine, ChristopheWed, 16 Nov 2016 21:01:29 GMTBulk high-temperature superconducting hollow cylinders used for magnetic shielding: effect of an initial trapped field on the shielding performances.http://hdl.handle.net/2268/203419
Title: Bulk high-temperature superconducting hollow cylinders used for magnetic shielding: effect of an initial trapped field on the shielding performances.
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<br/>Author, co-author: Wera, Laurent; Fagnard, Jean-François; Hogan, Kevin; Vanderheyden, Benoît; Vanderbemden, Philippe
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<br/>Abstract: Bulk High-Temperature Superconductors (HTS) can be used as efficient passive magnetic shields with performances exceeding those of conventional ferromagnetic materials. The most common geometry for a superconducting shield is a bulk hollow cylinder. In this work, we investigate the magnetic shielding properties when the tube is not in the virgin state. Such a situation happens in practice when the tube has been initially subjected to a first magnetic field. The induced superconducting currents that are flowing in the tube generate a trapped magnetic moment which may deteriorate the shielding of a second field. Here we study experimentally how an initial trapped moment affects the shielding of a magnetic field, when they are both perpendicular to each other. In particular, we focus on the effect of an axial trapped moment on the transverse shielding performances and on the effect of a transverse trapped field on the axial or the transverse shielding performances. Finally, we show how the pristine state of the tube can be restored when applying an external field of adequate amplitude. The consequence for practical applications is that it is possible to recover shielding properties similar to those obtained in the virgin state without heating up the shield above its critical temperature TC.Tue, 15 Nov 2016 07:43:43 GMTNon-destructive measurements of the volume magnetic behavior of large bulk GdBCO single domains and ferromagnet/superconductor structureshttp://hdl.handle.net/2268/203373
Title: Non-destructive measurements of the volume magnetic behavior of large bulk GdBCO single domains and ferromagnet/superconductor structures
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<br/>Author, co-author: Vanderbemden, Philippe; Egan, Raphael; Morita, Mitsuru; Teshima, Hidekazu; Nariki, Shynia; Vanderheyden, Benoît; Fagnard, Jean-François
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<br/>Abstract: The present work deals with magnetic measurements on bulk large grain GdBa2Cu3O7 (GdBCO) single domains using a recently constructed bespoke magnetometer [Rev. Sci. Instrum. 86 025107 (2015)]. The device enables the measurement of magnetic moments as large as 1 Am^2 (1000 emu) on large bulk samples up to 20 mm diameter at 77 K. This extends significantly the accessible measurement range of “off-the shelf” magnetometers (e.g. SQUID, VSM). Unlike Hall probe mapping, the measured signal is representative of the superconducting currents flowing across the entire height of the sample. Since the device is based on a flux extraction technique and does not include any Hall probe, another advantage is that no gap between a Hall probe and the sample needs to be taken into account to interpret the results.
In the present work we first show how the dimensions of the sensing coils and integration bounds are chosen in such a way the magnetometer is sensitive to dipolar magnetic moment of the sample, while being insensitive to moments of higher order. Next we study the relaxation of the trapped magnetic moment under various magnetization processes. The sensitivity of the device allows small variations of m (e.g. ~ 2% for 1 hour) to be recorded. We show experimentally that the relaxation of the magnetic moment of the whole sample is reduced strongly if the superconductor is not fully magnetized, either in field cooled (FC) or zero-field cooled (ZFC) conditions. The practical consequence is that an abnormally slow magnetic relaxation (large E-J power law exponent n) under a conventional magnetization procedure indicates that the bulk superconductor could be magnetized further.
In a second set of experiments, we study the increase of magnetic moment of a bulk superconductor when it is attached to a soft ferromagnetic disk. We also examine the irreversible demagnetization of these structures when subjected to crossed magnetic fields and compare to the magnetic moment of a classical (Nd-Fe-B) permanent magnets in the same conditions.
Acknowledgements: This work is part of an "Action de Recherches Concertees" grant (ARC 11/16 -03) from the "Communaute Francaise de Belgique".Sun, 13 Nov 2016 14:27:16 GMTProcessing and applications of (RE)BCO and MgB2 bulk superconductors: an introduction to the special issuehttp://hdl.handle.net/2268/203372
Title: Processing and applications of (RE)BCO and MgB2 bulk superconductors: an introduction to the special issue
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<br/>Author, co-author: Vanderbemden, Philippe; Cardwell, D A; Freyhardt, H C; Vanderheyden, Benoît
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<br/>Abstract: Preface of the Superconductor Science and Technology special issue "Focus on processing and applications of (RE)BCO and MgB2 bulk superconductors". This special issue focuses on contributions from the 9th International Workshop on Processing and Applications of Superconducting (RE)BCO Large Grain Materials (PASREG 2015). The workshop was held at the University of Liège, Belgium on 02–04 September, 2015, as a satellite conference of the European Conference on Applied Superconductivity (EUCAS 2015). The Chairman was Philippe Vanderbemden; Benoît Vanderheyden, David Cardwell, and Herbert C Freyhardt served as Co-Chairmen. PASREG 2015 was the latest in a series of international workshops previously held in Cambridge, UK (1997), Morioka, Japan (1999), Seattle, USA (2001), Jena, Germany (2003), Tokyo, Japan (2005), Cambridge, UK (2007), Washington D.C., USA (2010), and Tainan, Taiwan (2012).Sun, 13 Nov 2016 14:14:39 GMTMagnetic shielding properties of a cut superconducting hollow cylinder : modelling and experimenthttp://hdl.handle.net/2268/203371
Title: Magnetic shielding properties of a cut superconducting hollow cylinder : modelling and experiment
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<br/>Author, co-author: Vanderbemden, Philippe; Elschner, Steffen; Hobl, A; Bock, J; Vanderheyden, Benoît; Fagnard, Jean-François
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<br/>Commentary: This paper has been published in Superconductor Science and Technology 25 (2012) 104006Sun, 13 Nov 2016 13:49:03 GMTNon-destructive measurements of the volume magnetic properties of large bulk (RE)BCO superconductors and hybrid ferromagnet/superconductor structureshttp://hdl.handle.net/2268/203370
Title: Non-destructive measurements of the volume magnetic properties of large bulk (RE)BCO superconductors and hybrid ferromagnet/superconductor structures
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<br/>Author, co-author: Vanderbemden, PhilippeSun, 13 Nov 2016 13:31:54 GMTOverview of magnetism activities at the Measurements and Instrumentation laboratory of the University of Liegehttp://hdl.handle.net/2268/203368
Title: Overview of magnetism activities at the Measurements and Instrumentation laboratory of the University of Liege
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<br/>Author, co-author: Vanderbemden, PhilippeSun, 13 Nov 2016 12:08:46 GMTElectric charging of bodies and electrostatic discharges: Basic notionshttp://hdl.handle.net/2268/203367
Title: Electric charging of bodies and electrostatic discharges: Basic notions
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<br/>Author, co-author: Vanderbemden, PhilippeSun, 13 Nov 2016 11:58:43 GMTBehaviour of bulk superconducting trapped field magnets subjected to magnetic fields with a transverse componenthttp://hdl.handle.net/2268/203365
Title: Behaviour of bulk superconducting trapped field magnets subjected to magnetic fields with a transverse component
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<br/>Author, co-author: Vanderbemden, Philippe; Caps, Hervé; Vanderheyden, Benoît; Fagnard, Jean-François
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<br/>Abstract: Bulk superconductors can be used as trapped field magnets with unprecedented performances. Such trapped field magnets find a variety of engineering applications, in particular for brushless rotating machines and levitation devices. Compared to conventional permanent magnets, however, the magnetic field generated by a superconducting trapped field magnet is much more sensitive to the presence of an external field that is not perfectly aligned with the superconductor magnetic moment, i.e. when the external field has a transverse component. A situation where the superconductor experiences a magnetic field with a transverse component is likely to happen several times during running operation of the device. As an example, in a “trapped flux” synchronous machine, any variation of the load of the shaft may lead to a slight misalignment of the magnetic moment of the superconductor (placed in the rotor) with respect to the rotating field (generated by the stator). In such a situation, the superconductor is subjected to a rotating field, and the situation is likely to be different from a situation where the superconductor is subjected to a pure transverse field. In the present work, we aim at examining different scenarios (i.e. transverse or rotating) where the trapped field magnet is subjected to a transverse component. These configurations are examined both experimentally and numerically. The numerical model is used to determine the distribution of currents in the cross-section of the superconductor. We examine the conditions where the rotating field leads to a partial remagnetization of the sample and is therefore less detrimental that the application of a pure transverse field. We also show that the magnetic moment of the sample may behave differently that the field at the surface of the superconductor. Finally, we investigate the behavior of structures where the superconductor is attached to a thin ferromagnetic disk, and show the beneficial effect of such hybrid structures compared to the superconductor alone.
Acknowledgements : The research was funded through the University of Liège (ULg) and an ARC grant for Concerted Research Actions, financed by the French Community of Belgium (Wallonia-Brussels Federation), under reference ARC 11/16-03. We greatly acknowledge M. Morita, S. Nariki and H. Teshima
from Nippon Steel & Sumitomo Metal Corporation, Futtsu, Chiba.Sun, 13 Nov 2016 11:44:12 GMTSuperconductors used as trapped field magnets : investigation of hybrid structures combining superconducting and ferromagnetic materialshttp://hdl.handle.net/2268/203364
Title: Superconductors used as trapped field magnets : investigation of hybrid structures combining superconducting and ferromagnetic materials
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<br/>Author, co-author: Vanderbemden, Philippe; Fagnard, Jean-François; Caps, Hervé; Vanderheyden, Benoît; Philippe, Matthieu
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<br/>Abstract: In addition to their unique ability to carry electric currents without loss, superconductors are able to trap significant magnetic flux densities at low temperature. In so-called type-II irreversible superconductors, these properties are due to the pinning of individual flux lines (vortices) by defects at the nanoscale level. In this talk the influence of pinning on the magnetic properties of bulk superconductors will be explained and illustrated, with the emphasis placed on how pinning can be exploited to produce “trapped field magnets” for practical applications. We will then show how the properties of these trapped field magnets are enhanced when superconductors (SC) are combined to soft ferromagnetic (FM) alloys [1,2]. In particular we investigate the properties of macroscopic FM/SC/FM structures where the superconductor is sandwiched between two ferromagnetic sections, one of each circular face. In particular we show how the properties of the whole structure is influenced by the saturation magnetization and the geometry of the ferromagnetic material.
References:
1. M P Philippe, J-F Fagnard, S Kirsch, Z Xu, A R Dennis, Y H Shi, D A Cardwell, B Vanderheyden, and P Vanderbemden, Magnetic characterisation of large grain, bulk Y–Ba–Cu–O superconductor–soft ferromagnetic alloy hybrid structures. Physica C: 502 (2014) 20-30.
2. M P Philippe, M D Ainslie, L Wera, J-F Fagnard, A R Dennis, Y H Shi, D A Cardwell, B Vanderheyden, and P Vanderbemden, Influence of soft ferromagnetic sections on the magnetic flux density profile of a large grain, bulk Y–Ba–Cu–O superconductor. Superconductor Science and Technology: 28 (2015) 095008.Sun, 13 Nov 2016 09:59:52 GMTMagnetic shielding with bulk high-temperature superconducting hollow cylinders: improvement of the shielded volume and investigation of sequential orthogonal applied fieldshttp://hdl.handle.net/2268/203363
Title: Magnetic shielding with bulk high-temperature superconducting hollow cylinders: improvement of the shielded volume and investigation of sequential orthogonal applied fields
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<br/>Author, co-author: Vanderbemden, Philippe; Hogan, Kevin; Wera, Laurent; Vanderheyden, Benoît; Fagnard, Jean-François
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<br/>Abstract: Due to their ability to trap magnetic fields that exceed the saturation magnetization of conventional ferromagnets, bulk high-temperature superconductors have great potential to act as efficient passive magnetic shields. Shielding efficiency is usually demonstrated in bulk hollow cylinders. One of the main drawbacks of this geometry is that the shielding is only effective in the central region of the tube and decreases towards the tube extremities because of the field penetration through the open ends. In order to improve the performances at tube extremities and hence increase the shielded volume, the tube should be closed using e.g. a superconducting cap. Gaps or holes, however, are needed for allowing connections between the inner part of the tube and the external world. In this communication we examine the shielding efficiency and volume when a superconducting tube is closed either at one extremity or at both extremities. The effect of the gap size between the cap and the tube is also studied. Next we examine more complex magnetic shielding configurations where an external magnetic field is applied first one direction and a second field is subsequently applied along another (perpendicular) direction. We discuss the influence of pre-existing shielding supercurrents on the magnetic shielding properties.Sun, 13 Nov 2016 09:42:43 GMTCharacterization of superconductor magnetic properties in crossed magnetic fieldshttp://hdl.handle.net/2268/203362
Title: Characterization of superconductor magnetic properties in crossed magnetic fields
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<br/>Author, co-author: Vanderbemden, Philippe
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<br/>Abstract: This chapter deals with the characterization of the magnetic properties of superconductors which are subjected to magnetic fields that have been applied along two orthogonal directions, which is commonly referred to as a “crossed” magnetic field configuration. The purpose of this chapter is to describe the techniques that are useful to perform crossed field experiments, with an emphasis placed on practical aspects that are useful for designing the system and for understanding the measured data. This chapter is organized as follows. In Section 2, the key terms involved in the literature dealing with crossed field effects are defined. Section 3 deals with experimental methods and some key parameters will be outlined. In Section 4, practical conclusions will be drawn and next challenges in this area will be discussed.Sun, 13 Nov 2016 09:21:18 GMTBrandt model: applications in magnetic shielding and in magneto-thermal phenomenahttp://hdl.handle.net/2268/203241
Title: Brandt model: applications in magnetic shielding and in magneto-thermal phenomena
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<br/>Author, co-author: Vanderheyden, Benoît
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<br/>Abstract: In this talk, I illustrate two applications of the Brandt model to calculate magnetic shielding for high-Tc superconducting tubes and the self-heating of superconducting pellets, in each case subjected to an axial field. For magnetic shielding, the model is shown to faithfully reproduce the magnetic field measured along the axis and to exhibit the expected frequency scaling laws. End effects are further studied in cases where the shielding vessel is closed at its extremities, in order to increase the shielded volume. For self-heating, the Brandt model is extended to include the heat equation and heat transfer to a cryogenic fluid. The model reproduces the experimentally determined temperature profiles.Tue, 08 Nov 2016 16:05:54 GMTBig data, machine learning, and optimization, for power systems reliabilityhttp://hdl.handle.net/2268/203240
Title: Big data, machine learning, and optimization, for power systems reliability
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<br/>Author, co-author: Wehenkel, Louis
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<br/>Abstract: How to combine physical models with
observational data for ensuring power systems reliability, by leveraging simulation,
optimisation, and machine learning.Tue, 08 Nov 2016 16:04:55 GMTImproving the performance of trapped field magnets made of drilled bulk high-temperature superconductors by filling the holes with a soft ferromagnetic material.http://hdl.handle.net/2268/203239
Title: Improving the performance of trapped field magnets made of drilled bulk high-temperature superconductors by filling the holes with a soft ferromagnetic material.
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<br/>Author, co-author: Lousberg, Grégory; Fagnard, Jean-François; Ausloos, Marcel; Vanderbemden, Philippe; Vanderheyden, Benoît
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<br/>Abstract: The field trapped in a drilled bulk high-temperature superconductor
(HTS) is shown to be enhanced when the holes are filled with a powder
of a soft ferromagnetic material. Characterizations based on Hall
probe mapping and magnetization measurements are used and show an
increase of the trapped magnetic field after impregnation. These
results are examined with the help of a 3D finite element model, where
the ferromagnet material has a simplified, linear, constitutive law in
order to keep a manageable number of mesh nodes. Although such an
approach is a first-order approximation, it already confirms the
experimental observation and indicates a maximum increase of the
magnetic flux of 40 %.Tue, 08 Nov 2016 16:04:10 GMT